iceq on "[video explanation] can't login and can't upgrade manually"

Hi.
I am running WordPress Multisite/Network and I can't log in anymore, nor can I upgrade manually.
I wasn't sure I can explain it in words, but in this video I have explained exactly what I am having.
https://youtu.be/EN_K37CLzbk

Please see it and thanks in advance for your help.

(dear mod: I posted another topic only about the login issue, this one is about manual upgrade errors, so it's not a duplicate, please don'e delete)

Edit
For those who don't want/cant see the video:
The issue is not being able to login.
In the video I show 4 steps I took to resolve my issue, all of them fail:
1- upgrade manually by copying over all new WP 4.5.1 files to my existing WP 4.4.2 (excluding wp-config.php and wp-content folder).
Result: blog fails to load with an error in the wp-widgets.php file.

2- upgrade manually by copying only wp-admin folder. Blog loads, but same login failure issue.

3- upgrade manually by copying only wp-admin and wp-includes folder (excluding all root folder files and wp-content folder).
Result: blog fails to load with an error in the default-widgets.php file.

4- upgrade manually by copying only new wp-admin folder and new wp-settings.php file .
Result: blog fails to load with an error in the default-widgets.php file.

Thanks